In the gas insulation device, an insulation gas is encapsulated in a space between a metal tank at ground potential and a conductor which is installed in the tank and across which a voltage is applied, whereby insulation performance is secured.
However, when a tiny metal foreign substance is mixed in the tank, the metal foreign substance is charged and moved in a reciprocating manner in a radial direction in the tank due to the influence of the electric field generated by the energized conductor, and a decrease in the withstanding voltage can be caused. Thus, it is necessary to control the behavior of the metal foreign substance in the tank.
A conventional gas insulation device is designed in such a manner that an insulating coating material is applied to an inner surface of a tank and movement of an electric charge from the inner surface of the tank to a metal foreign substance is controlled to prevent an electric charge having an opposite polarity to a conductor from being accumulated in the metal foreign substance; to control floating of the metal foreign substance due to electric attraction force that affects the metal foreign substance becoming larger than weight of the metal foreign substance; and to prevent the metal foreign substance from being attached to a conductor and causing a flashover.
Also, in Patent Literature 1, a gas insulation device in which a coating material containing a zinc oxide (ZnO) having a non-linear resistance characteristic is applied to an inner surface of a tank is described.
Also, in Patent Literature 2, a technology of applying non-linear resistance coating on a barrier insulator is described as a coating technology in a gas insulation device.